Metal Oxide Nanoparticle Stock Suspension Preparation and Aggregation Kinetics Measurement Dr. Arturo Keller

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1 Protocol Project Title: PI: Theme: Project: 12 Version Number: 1.0 Metal Oxide Nanoparticle Stock Suspension Preparation and Aggregation Kinetics Measurement Dr. Arturo Keller Production Start Date: December, 2008 Version 1.0 Date: Oct., 2011 Authors: Department: Fate, transport, exposure and life cycle analysis Dongxu Zhou and Arturo Keller Bren School, UCSB Contact Phone # s: (805) Contact keller@bren.ucsb.edu Reviewed/Revised by: Ivy Ji This protocol has been published in whole or in part in the following journal articles (please provide complete citation): Keller, A.A., Wang, H., Zhou, D., Lenihan, H.S., Cherr, G. Cardinale, B.J., Miller, R., Ji, Z Stability and Aggregation of Metal Oxide Nanoparticles in Natural Aqueous Matrices. Environ. Sci. Technol. (2010) 44: , DOI: /es902987d Zhou, D., Keller, A., Role of morphology in the aggregation kinetics of ZnO nanoparticles. Water Research, 2010, 44(9), B.J.R. Thio, Zhou, D, Keller, AA. Influence of natural organic matter on the aggregation and deposition of titanium dioxide nanoparticles. J. Hazard. Mater. (2011), doi: /j.jhazmat Summary This protocol describes the protocol for (1). preparing metal oxide nanoparticle suspension in deionized water; (2). conducting aggregation kinetics experiments of metal oxide nanoparticles; 1/6

2 (3). conducting adsorption experiments between natural organic matter and metal oxide nanoparticles. Background and Project Goals Particle size of nanoparticles influences not only their environmental transport but also their toxicity. In natural aquatic systems, NPs tend to aggregate into larger particles tens or hundreds of times bigger than their primary particles. Therefore, the knowledge of how NPs aggregate and which factors play crucial roles in their aggregation is a necessity for studying NPs human toxicity and ecotoxicty. The goal of this project is to understand the influential factors of nanoparticle aggregation in aqueous media and to provide nanotoxicologists with knowledge of what particle size should they expect under natural conditions as well as the potential particle size change under their experimental conditions. Materials & Reagents Materials/Reagents/Equipment Disposables Conical centrifuge tubes (50 ml) 20mL glass scintillation vials Round glass cells for DLS Disposable 4mL cuvette Vendor Corning Life Sciences Wheaton Brookhave Instruments Fisher Scientific Stock Number BI-RC Reagents ZnO nanoparticle powders CeO 2 nanoparticle powders TiO 2 nanoparticle powders (P25) HCl NaOH Natural Organic Matter Borate Phosphate Meliorum Technologies Meliorum Technologies Evonik Degussa EMD Chemicals Inc EMD Chemicals Inc International Humic Substances Society Fisher Scientific Fisher Scientific SA MSX R101N A SB Equipment Dynamic Light Scattering (BI-200SM) Sonication bath (Branson 2510) Spectrophotometer (BioSpec 1601) Brookhaven Misonix Shimadzu 2/6

3 Environmental Health & Safety Nanoparticles (dry powders) handling has to be done in chemical fume hood and with N95 filter mask. Scientists performing this procedure must wear a lab coat and gloves. In situations where there might be a chance of an accidental splash to the eyes, safety glasses must be worn. Please refer to the Nanotoolkit produced by the California Nanosafety Consortium of Higher Education for recommendations regarding safe handling and disposal of nanomaterials. Prior to suspension of the nanoparticles, use engineering controls, work practices, and PPE as specified for Category 2 (Moderate Exposure Potential); after suspension, use use engineering controls, work practices, and PPE as specified for Category 1 (Low Exposure Potential) as specified in the Nanotoolkit. As described in the Nanotoolkit, NIOSH has determined that workers may be at risk of developing adverse respiratory health effects if exposed to certain nanomaterials for a working lifetime at the upper limit of quantitation (LOQ) using NIOSH Method 5040, which is currently the recommended analytical method for measuring airborne CNTs. The LOQ for CNTs using NIOSH Method 5040 is 7 μg/m3. Animal data-based risk estimates from NIOSH indicate that workers may have >10% excess risk of developing early stage pulmonary fibrosis if exposed over a full working lifetime at the upper LOQ for NIOSH Method Until improved sampling and analytical methods can be developed, and until data become available to determine if an alternative exposure metric to mass may be more biologically relevant, NIOSH is recommending a REL of 7 μg/m3 elemental carbon (EC) as an 8-hr TWA respirable mass airborne concentration. a Likewise, NIOSH recommends airborne exposure limits of 2.4 mg/m3 for fine TiO2 and 0.3 mg/m3 for ultrafine (including engineered nanoscale) TiO2, as time-weighted average (TWA) concentrations for up to 10 hr/day during a 40-hour work week. These recommendations represent levels that over a working lifetime are estimated to reduce risks of lung cancer to below 1 in 1,000. The recommendations are based on using chronic inhalation studies in rats to predict lung tumor risks in humans. b Citations: a NIOSH. (2010). Occupational Exposure to Carbon Nanotubes and Nanofiber. Current Intelligence Bulletin. b NIOSH. (2011). Occupational Exposure to Titanium Dioxide. Current Intelligence Bulletin. 3/6

4 Workflow (1). Prepare nanoparticle stock suspension (Zhou and Keller, 2010) (2). Prepare electrolyte, buffer (borate and phosphate), and natural organic matter (NOM) stock solutions (3). Dilute nanoparticle stock by deionized water and add in borate buffer and electrolyte. If studying the effect of NOM, add in NOM stock as well. (4). Measure the aggregation kinetics by dynamic light scattering (DLS). (5). Quantify the adsorption of NOM onto metal oxide nanoparticles by isothermal adsorption experiments. (6). Monitor the sedimentation process of metal oxide nanoparticles by spectrophotometer. Procedure 1. Nanoparticle suspension sample preparation for aggregation studies (Zhou and Keller, 2010). An aliquot of nanoparticle stock suspension is withdrawn and sonicated for 10 min to redisperse particles (10 min sonication was found to be sufficient to break loose metal oxide nanoparticle agglomerates). Borate or phosphate buffer (depending on the desired ph) is added to achieve a final buffer concentration of 1 mm. A measured amount of Nanopure water is then used to dilute the sample so that the final concentration of metal oxide NPs is 100 mg/l. A desired amount of electrolytes is added to the sample immediately before a DLS measurement is started. Electrolyte concentration varies from run to run so that the critical coagulation concentration can be determined. 2. Procedure of DLS measurement Aggregation kinetics is measured using time-resolved dynamic light scattering (DLS) (BI-200SM, Brookhaven Instrument, Holtsville, NY) with a 633 nm laser source. The detection angle is set to 90. Temperature of the DLS sample chamber is controlled at 25 C by a water bath. Before each set of experiments, decaline bath is filtered for 5 min to remove dust. Immediately after adding the desired amount of electrolytes (electrolyte concentration varies from run to run, and the typical range is 1mM to 200mM) to a sample, DLS measurements are started. Data are 4/6

5 collected at s intervals, and the intensity-weighted hydrodynamic radius is determined by second- order cumulant analysis. Data collection is continued until a 50% increase in the hydrodynamic radius is observed. 3. Adsorption experiment procedure The adsorption of NOM onto metal oxide nanoparticle surfaces is quantified by batch experiment using a bottle-point technique. Desired amounts of metal oxide stock suspension and adsorbate stock solution are added into 20 ml glass vials. A NaCl solution was used to adjust the IS as needed and a borate buffer of 1 mm final concentration was used to maintain the desired ph. Then deionized water with a preadjusted ph is used to dilute the system to the target concentrations. All samples were produced in duplicates including control. After this, the samples are agitated on a roller at 60 rpm for 24 h. Preliminary results showed this was sufficient to reach adsorption equilibrium. The samples are centrifuged at 15,180g for 5 min and the supernatant is analyzed for adsorbate concentration by measuring the light absorbency at 254 nm (BioSpec 1601, Shimadzu, MD). A NOM calibration curve was created so that the spectrophotometer reading can be converted to NOM concentration. 4. Sedimentation experiment procedure Before an experiment, the stock dispersion was sonicated for 10 min. The stock dispersion was then added to the water samples to achieve the target concentrations. The dynamic aggregation process was monitored using a UV-vis spectrophotometer (BioSpec 1601, Shimadzu, MD), measuring the sedimentation of the nanoparticles in different waters at various MeO concentrations via time-resolved optical absorbence (CeO2 at 321 nm, TiO2 and ZnO at 378 nm). Optical absorbence was measured every 6 min for 360 min. The experiments were run in duplicate or triplicate. Reagent/Stock Preparation (1). Nanoparticle stock preparation (Zhou and Keller, 2010) 0.05 g metal oxide powder is added into 50 ml deionized water and sonicated by a sonication bath for 30 min. (preliminary experiment shown that 30mins was the optimum sonication time 5/6

6 to achieve minimal particle size) The stock is let settle over night. The supernatant is then withdrawn and stored as stock suspension. Before use, aliquots of the stock solution are resonicated for 10 min and diluted into the desired concentration. The stock suspension is freshly prepared everyday. Nanoparticle dry powders are handled in fume hoods. (2). NOM stock preparation Suwannee River natural organic matter (NOM) was obtained from the International Humic Substances Society. A 200 mg/l NOM stock solution was prepared by mixing a known amount of NOM with deionized water, adjusting the solution ph to 8 to facilitate dissolution, and stirring overnight. (3). Acid, base, and buffer preparation HCl (0.1 M and 0.01 M) is prepared by diluting concentrated HCl solution (37%) to the desired concentration by deionized water. NaOH (0.1 M and 0.01 M), boric acid (200 mm), and phosphate (200mM) are prepared by weighing appropriate amount of dry powder and then dissolve them in deionized water. All the solutions are filtered via 0.22 mm PVDF filters to avoid potential interference in the light scattering experiments. SOP Approval DEPARTMENT APPROVED BY DATE Principal Investigator Arturo Keller 6/6